Modern life causes a disruption to natural biological rhythms in many ways. One of these ways is shift work. Shift work can be considered any scheduled work outside the 'normal' daytime hours of 7am to 7pm.
- It can either be fixed - regular day, evening or night shifts.
- Or rotating - a combination or cycle of these shifts.
Shiftwork disrupts our natural patterm of behaviour so that workers have difficulty establishing a regular circadian rhythm of day-night activity.
- The most taxing shift work schedules are those that go against the body's natural inclination to adapt to a longer day of about 25 hours. And those that include night work.
- If shift work schedules are to rotate then it is best if they rotate in a clockwise rather than anti-clockwise direction.
- The problem with anti-clockwise rotating shifts is hat they cause greatest disruption to circadian rhythms and result in shortened sleep.
Shift work (Cont.)
- Another problem with anti-clockwise shift work shedules is that in effect the body never adapts to its current rhythm before it has to readjust to a new one.
Czeisler et al (1985)
- Devised a new work schedule for police officers in phillidelphia.
- This new schedule involved a change in rotation length and a change in shift direction to clockwise.
- Significant benefits resulted - for example, accident in the night shift fell by 40% and officers reported a greater satisfaction in their personal lives.
A range of health problems has been associated with night and rotating shift work, such as hypertension, coronary heart disease and cancer.
In addition, sleep deprivation has been shown to cause deficits in cognitive and physical performance, and is associated with a range of serious health problem, resulting from disrupted metalbolism.
Shift work and health problems.
Knutsson et al (1999)
- Found that night shift work increases the risk of heart attack by 30% compared with that found in day workers.
- This was the case for both men and women who had been exposed to shift work for 16 to 20 years.
Kubo et al (2006)
- Suggest that people working rotating shifts are particularly vunerable to cancer.
- They studied the cancer risk in 14,052 Japanese male workers, controlling for lifestyle factors, such as smoking, drinking etc.
- They found that the men who worked some kind of night shift were FOUR times as likely to develop prostate cancer han men who worked fixed day shifts.
Shift work and health problems. (Cont.)
HOWEVER...Schwartzbaum et al (2007)
- conducted a long term stody of the health of 3.2 million swedish workers.
- They comapre the incidence of cancer in occupational groups with at least 40% shift work and those that were in groups that has less yjam 30% shift work.
- The researchers found no relationship between shift work and increased rate of developing cancer.
HOWEVER...The study has been critised because of the was that it defined shift work and how it bombined many different jobs with different degrees of shift work
Schernhammer et al (2001)
- used data gathered as part of a 10 year study following the health of 78,562 US nurses (Accounting for potential variables, weight, alchohol consumption etc.)
- They found that the risk of breast cancer increased significantly with the number of years working rotating shifts.
Shift work and Melatonin?
Exposure to artificial light disrupts a natural rhyth, which appears essential for a range of physiological functions. One important hormone which has a very distinct pattern of production is melatonin.
- Melatonin concentrations in the body normally peak in the middle of the night. Exposure to light, wether natural or artificial , alters the release of melatonin so that almost none is produced.
- It has been found that it can take ober two weeks for lebels to recover after night tume light exposure and even then full recovery only occurs when there has been a period of contstant day-night circadian rhythm. (Zeitzer et al, 2000)
- Previous research also suggests that melatoni is also associated with anti-cancer properties.
Shift work and Melatonin? (Research.)
Schernhammer and Hankinson (2003)
- point out that blind women, who do not have their melatonin levels suppressed by light, experience a lower incidence of breast cancer.
Speigel and Sephton (2002)
- agree that cancer is associated with disruption of biological rhythms, they argue that this association is not due solely to a reduction of melatonin secretion.
- They suggest that increased risk is actually caused by disruption of diurnal rhythms in the hormone cortisol.
- This hormone, acoording the Speigel and Sephton, is related to early death from breast cancer.